A high-strength low-rare-earth-alloyed magnesium alloy via traditional hot-extrusion

A high-strength low-rare-earth-alloyed Mg−3.5Sm−2Yb−0.6Zn−0.4Zr alloy was processed by an ingot metallurgy process with hot-extrusion followed by artificial aging. The peak-aged sample exhibited a higher yield strength of 449 MPa than most of extruded Mg−Gd based alloy containing high RE content, and even is comparable to that of the T8-treated 2024 Al alloy. The studied alloy exhibited a typical bimodal microstructure, consisting of dynamically recrystallized (DRXed) grains with random textures and coarse unrecrystallized regions with strong basal fiber texture. In addition, the fragmented Mg5RE and Mg41RE5 phases distributed at extrusion stringers. Abundant of fine Mg3RE particles precipitated dynamically in DXRed regions, which restrains DRXed grains growth effectively by grain boundary pinning. Within the unDXRed regions, uniformly dense Mg3RE and Mg12RE nano-precipitates were observed. Also there were many basal dislocations and a few non-basal dislocations in unDXRed regions. Subsequent artificial ageing significantly enhanced the alloy's strength by introducing basal precipitates, although decreased the ductility slightly. Finally, the ultrahigh yield strength was revealed to be attributed to the combined effects of a strong basal fiber texture, a bimodal microstructure, and numerous precipitated particles. •A high-strength low-rare-earth-alloyed Mg−3.5Sm−2Yb−0.6Zn−0.5Zr (wt.%) alloy was successfully developed.•Ultrahigh yield strength of 449 MPa was achieved in this alloy.•Three texture components were found in the dynamically recrystallized regions.•Amounts of nanoscale particles dynamically precipitated in the unrecrystallized regions.•The underlying causes of ultrahigh yield strength were discussed in detail.